Electrophotographic element containing a barrier layer comprising block copolycarbonates

ABSTRACT

ELECTROPHOTOGRAPHIC ELEMENTS COMPRISED OF A SUPPORT, AN ELECTRICALLY CONDUCTING LAYER, A NOVEL BARRIER LAYER AND A PHOTOCONDUCTIVE INSULATING LAYER. THE NOVEL BARRIER LAYERS ARE FORMED OF BLOCK COPOLYCARBONATES HAVE ONE RECURRING UNIT CONTAINING AN ALKYLIDENE DIARYLENE MOIETY AND ANOTHER RECURRING UNIT CONTAINING AN OXYTETRAMETHYLENE MOIETY THESE BARRIER LAYERS HAVE IMPROVED ADHESION WITH CONTIGUOUS LAYERS.

United States Patent 3,554,742 ELECTROPHOTOGRAPHIC ELEMENT CONTAIN- ING A BARRIER LAYER COMPRISING BLOCK COPOLYCARBONATES Eugene P. Gramza and Edmond S. Perry, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Continuation-impart of application Ser. No. 717,372, Mar. 29, 1968. This application Feb. 18, 1970, Ser. No. 12,470

Int. Cl. G03g 5/00, 5/04, 5/06' US. Cl. 961.5 7 Claims ABSTRACT OF THE DISCLOSURE This is a continuation-in-part application based on US. application Ser. No. 717,372, filed Mar. 29, 1968.

This invention relates to electrophotography and in particular to novel photoconductive elements and structures useful in electrophotography and which have improved barrier layers.

Electrophotographic imaging processes and techniques have been extensively described in both the patent and other literature, for example, US. Pats. Nos. 2,221,776; 2,277,013; 2,297,691; 2,357,809; 2,551,582; 2,825,814; 2,833,648; 3,220,324; 3,220,831; 3,220,833 and many others. Generally, these processes have in common the steps of employing an electrophotographic element which is prepared to respond to imagewise exposure with electromagnetic radiation by forming a latent electrostatic charge image. A variety of subsequent operations, now well known in the art, can then be employed to produce a permanent record of the image.

One type of unitary photooonductive element particularly useful in electrophotography is generally produced in a multi-layer structure. Such an element is prepared by coating a layer of an insulating photoconductive composition onto a film support previously overcoate-d with a layer of conducting material. In addition, an insulating or barrier layer is interposed between the conducting material and the photoconductive composition.

One purpose of the barrier layer in an electnophotographic element is to reduce the charge leakage in the absence of activating radiation. Such charge leakage is generally referred to as dark decay. On the other hand, a suitable barrier layer must not prevent proper charge dissipation in the presence of activating radiation. The barrier layer also helps to reduce the variation in performance upon repeated use of an element. Such a variation in performance of an electrophotographic element upon repeated use is known as charge fatigue. In essence, the function of a Ibarrier layer is to prevent passage of charge 3,554,742 Patented Jan. 12, 1971 from the conductive layer to the photooonductive insulating layer thus preventing unwanted discharge of the photoconductive layer.

However, problems are often encountered with prior electrophotographic elements of this type in that there is often considerable difliculty in obtaining good adhesion between the conducting layer and the barrier layer or between the photoconductive insulating layer and the barrier layer. Because of the lack of good adhesion between layers, many prior electrophotographic elements could not be substantially flexed without causing the layers to separate in various places.

It is, therefore, an object of this invention to provide electrophotographic elements having new barrier layers which have improved adhesion to substrates.

It is a further object of this invention to provide novel electrophotographic elements having new barrier layers to which overcoated layers readily adhere.

Still another object of this invention is to provide novel electrophotographic elements capable of forming good quality images having low background.

A further object of this invention is to provide novel electrophotographic elements capable of being electrically charged in a positive or a negative mode.

These and other objects and advantages are accomplished in accordance with this invention with an electrophotographic element having a barrier layer comprised of a block copolycarbonate having one recurring unit containing an alkylidene diarylene moiety and another recurring unit containing an oxytetramethylene moiety. This barrier layer is positioned between a photoconductive layer and a conducting layer on a support.

The resinous materials useful in accordance with this invention are block copolymers comprising recurring carbonate units having the following formula:

ORCRO 1's 0 II C copolymerized with blocks composed of recurring units having the formula:

OCH2CH2CH2CH2)X O-]C wherein R represents a phenylene radical including substituted phenylene, for example, halo substituted phenylene radicals such as chlorophenylene, dibromophcnylene, dichlorophenylene, etc., and R and R ,"when taken separately, can each represent a hydrogen atom, a lower alkyl radical having 1 to 6 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, etc., and when taken together with the carbon atom to which they are attached, R and R can represent the canbon atoms necessary to form a cyclic hydrocarbon typically having 4 to 10 carbon atoms in the nucleus such as cyclobutyl, cylohexyl, and including polycyoloalkanes such as norbornyl and wherein x is a positive integer such that the molecular weight of the recurring moiety about 50 to 70% by weight of the recurring unit (II) above.

Particularly useful materials for forming the barrier layers of this invention are block copolycarbonates comprised of recurring units having the following formula:

copolymerized with blocks composed of recurring units having the Formula II above, wherein R R R and R each represent a hydrogen atom or a chlorine atom and R and R when taken separately can each represent a lower alkyl radical of from 1 to 3 carbon atoms and when taken together with the carbon atom to which they are attached, R and R can represent the carbon atoms necessary to form a polycycloalkane. The preparation of compounds of this type is given in an article by K. P. Perry, W. J. Jackson, Jr. and J. R. Caldwell in volume IX of the Journal of Applied Polymer Science at page 3451 (1965). In general, the preparation involves the addition of phosgene to a pyridine solution of poly(tetramethylene ether) glycol and bisphenols containing an alkylidene moiety. Phosgene is typically added in a 10 to 30 molar excess. The temperature of the reaction is usually maintained at about 20 to 30 C.

The electrophotographic elements of the present invention can be formed on a wide variety of support materials. Suitable support materials would include glass; wood; paper, including coated paper such as polyethyleneor polypropylene-coated paper, baryta coated paper, etc.; polymeric materials such as cellulose acetate, poly(ethylene terephthalate), polyethylene, polypropylene, etc.; and other known support materials.

The conductive coating which is placed on the support can be formed in a variety of ways and from a number of materials. One method of applying such a conductive coating is by evaporation techniques such as described in U.S. Pat. No. 2,756,165. Another suitable method of forming the conductive layer is by coating onto the support a solution of a conductive or semiconductive material and a resinous binder in a volatile solvent and evaporating the solvent to leave a conductive layer. U.S. Patent No. 3,245,833 discloses methods for accomplishing this latter technique.

Particularly good conductive layers for use with the present barrier layers utilize a metal-containing semiconductor compound such as cuprous iodide, silver iodide, etc. Conductive layers of this sort can be prepared as described in the above U.S. Pat. No. 3,245,833. In addition, conductive layers of metal-containing semiconductor compounds can be prepared by the imbibition techniques described in Gramza and Stahly copending U.S. application Ser. No. 717,386, entitled Electrophotographic Element and Process, filed Mar. 29, 1968. These metal-containing semiconductor compounds can be coated at a wide range of coverages with useful results being obtained at coverages of from about 4 to about 40 mg./ft. based on the dry weight of the semiconductor compound.

Similarly, the photoconductive layer in the present electrophotographic elements can be comprised of a variety of materials. Photoconductors suitable for use in the photoconductive layer can include inorganic, organic and organometallic materials. Useful photoconductors would include zinc oxide, titanium dioxide, organic derivatives of Group Na and Va metals such as those having at least one amino-aryl group attached to the metal atom, aryl amines, polyarylalkanes having at least one amino substituent, etc. The following Table A is a partial listing of U.S. patents disclosing a variety of organic photoconductive compounds and compositions which are useful in accordance with the present invention.

4 TABLE A U.S. Patent No.

Schlesinger 3,139,338 Schlesinger 3,139,339 Cassiers 3,140,946 Davis et al. 3,141,770 Ghys 3,148,982 Cassiers 3,155,503 Schlesinger 3,257,202 Sues et al. 3,257,203 Sues et al 2,257,204 Fox 3,265,496 Kosche 3,265,497 Noe et al. 3,274,000

The photoconductor is usually applied by forming a mixture with a polymeric binder material and coating the mixture over the barrier layer. The photoconductive layer can be applied by a variety of means such as spray coating, swirl coating, extrusion hopper coating, etc. Also the amount of photoconductor in the layer can be varied from about 10 to about 60 percent by weight of the total solids in the photoconductive layer.

The barrief layers of the present invention can likewise be applied in a variety of ways such as spray coating, dip coating, swirl coating, extrusion hopper coating, bead application on a continuous coating machine and the like. In addition, the coating coverage can be varied widely. Useful results are obtained at coverages of from about 0.04 to about 0.50 mg./ft. based on the dry weight of the resin. Preferred coverages range from about 0.05 to about 0.40 mg./ft.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 A 4 mil. poly (ethylene terephthalate) film base is coated with a coating solution containing 0.4 g. of a poly(vinyl formal) resin containing 5 to 7% poly(vinyl alcohol) and 40 to 50% poly(vinyl acetate), 0.4 g. of a polyisocyanate cross-linking agent containing 75% solids having about 13% isocyanate and 1% free tolylene diisocyanate in ethyl acetate and 2.4 g. of cuprous iodide dissolved in 96.8 g. of acetonitrile. This solution, which is prepared essentially in accordance with Example 16 of U.S. Patent No. 3,245,833, is coated from an extrusion hopper at a dry coverage of 12 mg./ft. to form a conducting layer. Next a clear resin solution comprised of 3.0 g. of poly(4,4'- isopropylidenediphenylcarbonate b tetrahydrofuran) [also referred to as poly(4,4-isopropylidenediphenylene carbonate-block-oxytetramethylene)] dissolved in 38.8 g. dichloromethane and 58.2 g. 1,2-dichloroethane is coated directly onto the cuprous iodide conducting coating at a dry coverage of 0.1 g./ft. The resultant overcoated conducting layer is referred to as composite layer A. Another clear resin solution prepared from 9.8 g. of cotton cellulose nitrate dissolved in 85.2 g. methyl alcohol, 2.3 g. nbutyl alcohol and 2.7 g. cyclohexanone is also coated by extrusion hopper directly on a similar cuprous iodide conducting coating at a dry coverage of 0.19 g./ft. These two layers together are referred to as composite layer B. Next, a high speed photoconductive layer prepared as described in copending U.S. application Ser. No. 674,006 in the name of Gramza, filed Oct. 9, 1967, is coated from an extrusion hopper onto composite layer A at a dry coverage of 1.4 g./ft. The photoconductive composition is prepared from 9.0 g. of polycarbonate resin formed from the reaction between phosgene and dihydroxydiarylalkane or from the ester interchange between diphenylcarbonate and 2,2-bis-4-hydroxyphenylpropane, 6.0 g. of 4,4-diethylamino-2,2-dimethyltriphenylmethane and 0.3 g. of 4-(4-dimethylaminophenyl) 2,6 diphenylthiapyrylium perchlorate in 51.0 g. of methylene chloride and 34.0 g. of 1,1,2-trichloroethane. The solution is then sheared in a high-speed blender for a period of time and coated onto layer A to give an aggregate of approximately 0.2 to 0.4 micron in size. The resulting three-layer coating is referred to as Photoconductive Element 1. Likewise, this same organic photoconductor solution is also coated by extrusion hopper directly on composite layer B at a dry coverage of 1.4 g./ft. This resulting three-layer coating is referred to as Photoconductive Element II.

Speed The electrophotographic speeds of the elements are then determined in the following manner. The element is electrostatically charged under a corona source until the sur- .'face potential, as measured by an electrometer probe,

reaches about 600 volts. The charged element is then exposed to a 3000 K. tungsten light source through a standard stepped density gray scale. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V0, to some lower potential, V, whose exact value depends on the actual amount of exposure in meter-candle-seconds received by the area. The results of these measurements are then plotted on a graph of surface potential V vs. log exposui'e for each step. The actual positive or negative speed of the element can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed arbitrarily selected value. Herein, unless otherwise stated, the actual positive or negative speed is the numerical expression of 104 divided by the exposure in meter-candle-seconds required to reduce the 600 volt charged surface potential to a value of 500 volts (100 volt shoulder speed) or to a value of 100 volts (100 volt toe speed). The positive and negative 100 volt shoulder and toe speeds are shown in Table I below.

Image Next, an electrical contact is provided on the conducting layer of Photoconductive Element 1. Then a receiving sheet, such as that disclosed in Gramza et al. U.S. application Ser. No. 673,544, filed Oct. 9, 1967, entitled Image Receiving Elements, is placed on a conductive metal plate. The photoconductive element and the receiver sheet are then placed face to face in close proximity in such a manner that there is approximately a 20 micron air gap between the surfaces of the two. The conductive metal plate is connected to the ground side of a power supply and the conducting layer of the photoconductive element is connected to the high voltage side of thefpower supply. The photoconductive element on top of the; receiving sheet and conducting plate are placed under a photographic microfilm enlarger, marketed by Eastman Kodak Co. under the name of Recordak MEB Enlarger, containing a microfilm negative in the film gate. A latent electrostatic image is placed on the receiver paper by the folowing procedure. A potential of -1500 volts D.C., with respect to ground, is applied to the conducting layer of the photoconductive element. One second after the beginning of the application of electrical potential, the photoconductive element is exposed for a period of one second. The intensity level at the photoconductor is three foot candles. The -l500 volt potential is applied throughout this exposure and is terminated one-half second after the exposure is completed. The power supply is then reversed so that a post-exposure potential of +1200 volts D.C., with respect to ground, is applied to the photoconductive element. The duration of this post-exposure potential is one second. 'Next, the photoconductive element and the receiving sheet are separated and the receiving sheet bearing the electrostatic image is developed by immersing in a positive polarity liquid electrophotographic developer of the type described in U.S. Patent No. 2,907,- 674. The resultant image is a positive appearing reproduction of the negative orginal, displaying dense, sharp, black characters with uniform low density in the background. This same procedure is again followed using Photoconductive Element H. The image quality is shown in Table I below.

6 Adhesion TABLE I v. toe

100 v. shoulder speed speed Photoconductive element Adhesion Print? quality Excellent Gooddensity,

low background.

II 8,000 8,000 2,500 3,500 Poor Low density,

high background.

*Average of 12 coatings.

EXAMPLE 2 A clear resin solution of 3.0 g. poly(4,4-norbornylidene- 2,2,6,6' tetrachlorodiphenylcarbonate-b-tetrahydrofuran) [also referred to as poly(4,4 norbornylidene- 2,2,6,6' tetrachlorodiphenylene carbonate-block-oxytetramethylene)] dissolved in 38.8 g. dichloromethane and 52.2 g. 1,2-dichloroethane is coated directly on a cuprous iodide conducting layer prepared as in Example 1. The resultant composite coating is then overcoated with the same organic photoconductor composition described in Example 1. The resulting three-layer coating is referred to as Photoconductive Element III and is evaluated as in Example 1. The results of this evaluation are summarized in Table II. The speed, adhesion properties and image quality are essentially the same as that achieved with Photoconductive Element I above.

TABLE II Photoconductive element 100 v. shoulder speed:

8000. 8000. 100 v. toe speed:

Adhesionexcellent. Print* qualitygood density, low background.

*Average of 12 coatings.

EXAMPLE 3 A lower speed photoconductive composition is prepared by dissolving 12.0 g. of the polycarbonate resin of Example 1, 3.0 g. of the amino-substituted triphenylethane of Example 1 and 0.075 g. of the thiapyrylium of Example 1 in 51.0 g. of dischloromethane and 34.0 g. of 1,1,2-trichloroethane. This solution is sheared as in Example 1 and the resultant aggregate size is about 0.1 micron when the solution is coated onto composite layers A and B of the first example. The resultant overcoated composite layers A and B are designated as Photoconductive Elements IV and V, respectively. These elements are then evaluated as in Example 1 and the results of this evaluation are shown in Table III below.

TABLE III 100 v. toe speed III.

100 v. shoulder speed Photoconductive element Adhesion Print" quality 800 Excellent- Good density,

low background.

800 Poor Low density,

high background.

*Average of 12 coatings.

copolymerized with blocks composed of recurring units having the formula:

wherein R represents a phenylene radical and R and R when taken separately, are each selected from the group consisting of a hydrogen atom and a lower alkyl radical and when taken together with the carbon atom to which they are attached, R and R represent the carbon atoms necessary to form a cyclic hydrocarbon radical and x is an integer such that the molecular weight of the recurring moiety {OCH2CH2CH2CH2 X is about 650 to 6500.

2. An electrophotographic element as in claim 1 wherein the block copolycarbonate comprises recurring units having the formula:

copolymerized with blocks comprising units having Formula II, wherein R R R and R are each selected from the group consisting of a hydrogen atom and a halogen atom and R and R when taken separately, each represents an alkyl radical of from 1 to 3 carbon atoms and when taken together with the carbon atom to which they are attached, R and R represent the carbon atoms necessary to form a polycycloalkane radical- 3. An electrophotographic element as in claim 1 wherein the polymeric material comprises poly(4,4-isopropylidene-diphenylene carbonate-block-oxytetramethylene) 4. An electrophotographic element as in claim 1 where in the polymeric material comprises poly(4,4'-norbornylident-2,2',6,6' tetrachlorodiphenylene carbonate blockoxytetramethylene).

5. An electrophotographic element comprising a support having coated thereon a conductive layer of a metal-containing semiconductor compound, said conductive layer having in continguous relationship therewith a barrier layer comprised of a block copolycarbonate comprising recurring units having the formula:

copolymerized with blocks composed of recurring units having the formula:

wherein R R R and R are each selected from the group consisting of a hydrogen atom and a halogen atom and R and R when taken separately, each represents an alkyl radical of from 1 to 3 carbon atoms and when taken together with the carbon atom to which they are attached, R and R represent the carbon atoms necessary to form a polycycloalkane radical and x is an integer such that the molecular weight of the recurring moiety is about 650 to 6500, and coated on said barrier layer a photoconductive layer containing an organic photoconductor.

6. An electrophotographic element as in claim 5 wherein the metal-containing semiconductor compound is cuprous iodide.

7. An electrophotographic element as in claim 6 wherein the barrier layer is comprised of a polymer selected from the group consisting of poly(4,4'-isopropylidenediphenylene carbonate-block-oxytetramethylene) and poly- (4,4-norbornylidene-2,2,6,6-tetrachlorodiphenylene carbonate-block-oxytetramethylene References Cited UNITED STATES PATENTS 2,986,467 5/1961 Kostelac et a1. 961 3,241,958 3/1966 Bornarth et al. 961 3,248,279 8/1966 Geyer l62138 3,265,496 8/1966 Fox 96-1 3,272,121 9/1966 Uber et al. 101-1492 3,298,831 1/1967 Lan et al. 96--1.5 3,403,116 9/1968 Ream et al. 2608 GEORGE F. LESMES, Primary Examiner J. C. COOPER III, Assistant Examiner US. Cl. X.R. 

